This application was filed under 35 U.S.C. 371, and is the U.S. National Stage of PCT/CZ00/00075, filed Oct. 11, 2000.
The present invention relates to a method of ethyl acetate synthesis by esterification of acetic acid with ethyl alcohol or by reaction of acetic anhydride with ethyl alcohol, which method uses catalytic distillation in a column, during which catalytic distillation a reaction on a catalytically active filling and a rectification and separation of reaction products take place simultaneously. The present invention relates also to equipment for carrying out this method.
Ethyl acetate is prepared by reaction of ethyl alcohol and acetic acid, which reaction produces, apart from ethyl acetate, also water. Alternatively, ethyl acetate can be prepared by reaction of acetic anhydride with ethyl alcohol, during which reaction, apart from ethyl acetate, also acetic acid is produced, which acetic acid is further esterified by another portion of ethyl alcohol. The esterification is an equilibrium reaction and is accelerated by the presence of acid catalysts. For this purpose, predominantly mineral acids are used, preferably sulfuric acid or, as an advancement, solid acidic catalysts. Such acidic catalysts are mainly the acidic ion exchangers, or eventually zeolites, or the so-called solid superacids, and so on.
According to prior art methods, the reaction is usually carried out so that a nearly equilibrium composition of reaction mixture is obtained in a reactor, which composition depends on the starting molar ratio of reacting components. The so obtained mixture is rectified in a column, distilling out a mixture having a composition close to the ternary heterogenic azeotrope containing ethyl alcohol, ethyl acetate and water. Because the amount of water produced by this reaction is greater than the amount of water distilled in the form of the azeotrope, the superfluous water is withdrawn from the column boiler together with the unreacted acetic acid. The so obtained acetic acid has to be regenerated by another distillation. The following distillation separation of the organic phase of the ternary azeotrope so obtained, i.e. first of all, separation of the unreacted ethyl alcohol from ethyl acetate, is of course very demanding, considering that it is a substantially non-ideal mixture where ethyl alcohol and ethyl acetate form a binary azeotrope, and apart from that they form a ternary azeotrope with water having minimal boiling point. From the water phase, which was separated from the distillate of the first column, the dissolved ethyl acetate and ethyl alcohol are then distilled out by means of another distillation column, and this mixture of alcohol and acetate is then returned into the process. A complex method of separating the esterification reaction components is the main disadvantage of the prior art methods mentioned. In case of methods using the mineral acids as catalyst, significant environmental and corrosion problems are also observed.
In principle, it is also known to carry out the esterification of acetic acid by ethyl alcohol in a distillation column either in the absence of a catalyst (Chem. Eng. Technol. 1997, 20, 182) or by feeding a homogenous catalyst, i.e. a mineral acid, together with one of the reaction components (Chemia Stosowana 1989, 33, 509). Also, use of a batch column was disclosed, which column is filled with particles of an acidic ion exchanger, whereby such particles act both as a catalyst and as a column packing (Separation Science and Technology 1992, 27, 613). Of course, the rate of a non-catalytic esterification is too low to allow industrial use. The reactive distillation using a homogenous catalyst feed brings about the above-mentioned corrosion problems and environmental disadvantages. The distillation column packed with free particles of acidic catalyst is inapplicable in an industrial process because of high hydrodynamic resistance and poor separation efficiency.
Accordingly, it is an object of the present invention to eliminate the drawbacks of the prior art methods.
A method of producing ethyl acetate by reaction of ethyl alcohol with acetic acid and/or acetic anhydride according to the present invention consists in that, in the presence of a solid acidic catalyst and during simultaneous distillation separation of reaction components, acetic acid or acetic anhydride or their mixture and ethyl alcohol are introduced separately in a molar ratio of 2:1 to 1:2.5 and in a quantity, expressed as total flow rate, of 0.1 to 10 hxe2x88x921 of the introduced components, based on unit volume of catalyst, into the system, in which system the reaction and the distillation separation are carried out in three zones, whereby in a reaction zone the reaction runs simultaneously with the distillation separation of components having different boiling points, and in two separation zones only the distillation separation of components takes place, whereby water produced as a by-product of the reaction, forming a low-boiling azeotropic mixture with ethyl acetate, distills completely or partially from the system. Thereafter, the distillate is cooled to 5 to 70xc2x0 C. and then water is separated from the ethyl acetate and other organic components of the distillate and is withdrawn from the system, whereas the organic components of the distillate, containing predominantly raw ethyl acetate, are partially returned back as reflux flow, whereby the feed stream of acetic acid and/or acetic anhydride and the ethyl alcohol feed are introduced into the system so that the acetic acid and/or acetic anhydride feeds are introduced into the reaction zone or above this zone into a place situated above the place of the ethyl alcohol feed, and the ethyl alcohol feed is introduced into the reaction zone or under this zone, whereby the ratio between the feed of the starting components into the column and the organic phase reflux flow into the column head is from 1:1 to 1:20 , and the residual unreacted acetic acid that can contain a part of the water produced by chemical reaction and that was not separated in the form of distillate is separated as the higher boiling bottom component. As catalyst, an acidic ion exchanger can be used, for example a sulfonated styrene-divinylbenzene copolymer containing 1 to 25% by weight of divinylbenzene with acidity 1 to 10 meq(H+)/g. However, any other acidic ion exchanging resins, or for example acidic zeolites and other known acidic catalysts, can also be used.
A preferable embodiment of this method is operated maintaining the following characteristics: molar ratio of acetic acid to ethyl alcohol is 1:1 to 1:0.45, or that of acetic anhydride to ethyl alcohol is 1:2 to 1:1.5; feed flow rate of input components, based on unit volume of catalyst, is 0.5 to 5 hxe2x88x921; and ratio of the input components fed into the reaction to the organic phase reflux flow is 1:1 to 1:20. Instead of a pure acetic acid or acetic anhydride feed or their mixture, a partially reacted mixture of acetic acid or acetic anhydride and ethyl alcohol can be used, so that the feed stream containing acetic acid can also contain ethyl acetate and/or water and/or unreacted ethyl alcohol.
The method according to the present invention is carried out using equipment comprising a column consisting of three zones, whereby the reaction zone, placed in the middle part of the column, contains solid acidic catalyst fixed on distillation trays or, in a preferable embodiment, anchored in the known types of oriented packings with internal channel structure, where the catalyst is fixed between two layers of inert porous material forming the structure of the packing. The bottom separation zone and the top separation zone comprise inert poured packings, which are the structured oriented packings of known designs or distillation built-in parts. The acetic acid and/or acetic anhydride feed pipeline is connected into the upper part of the reaction zone or above this zone, the ethyl alcohol feed pipeline is introduced into the bottom part of the reaction zone or under this zone, the column bottom is provided with a boiler, the draw-off of the unreacted acetic acid is provided in the column boiler or in the column bottom, and the upper part of the column is terminated by a head, which head is provided with a withdrawal of distillate vapors into a condenser, whereby a condensed distillate pipeline is provided transferring the condensed distillate into a separator, whereby the separator is provided with a withdrawal pipeline for removal of the distillate water phase in the bottom part, an outlet pipeline for draining of the reflux flow, and an outlet pipeline for withdrawal of the distillate organic phase.
It is apparent from the above-specified summary of the invention that the method according to the present invention makes obtaining a higher than equilibrium, nearly 100% conversion, of the starting components to ethyl acetate and water, possible. Especially, if ethyl alcohol is supplied with a slight stoichiometric deficit into the system, ethyl alcohol is converted to ethyl acetate nearly completely, which ethyl acetate is then obtained in the form of an easily separable mixture with water. The separation zones fulfill the function of separating reaction products, i.e. ethyl acetate and water, from the starting components, i.e. acetic acid and ethyl alcohol, and returning of said starting components back into the reaction zone, whereby ethyl acetate is separated together with water as a distillate continually, and, after separation from the organic phase of this distillate, the water phase containing mainly ethyl acetate is separated from the system and the organic part of the distillate is partially returned to the column as back flow and is partially drawn off.
The starting materials, i.e. acetic acid or acetic anhydride and ethyl alcohol, can be fed into the reaction zone either in stoichiometric ratio or with molar excess of acetic acid and/or acetic anhydride to convert nearly all the ethyl alcohol. If the method according to the present invention is carried out at atmospheric pressure, the temperature mode of the column is stabilized so that the temperature in the column head reaches 70 to 74xc2x0 C. Feed of the starting components into the column is carried out so that ethyl alcohol is introduced into a lower place of the column than the acetic acid and/or acetic anhydride feed. In a usual embodiment of this method, ethyl alcohol is fed under the catalytic zone or into its lower part. On the other hand, the feed containing acetic acid or acetic anhydride is fed above this zone or into its upper part.
Vapors passing away from the column head condense, producing a mixture, which mixture is cooled to 70 to 5xc2x0 C. and then separated into water and organic phases, whereby a part of the organic phase containing primarily ethyl acetate is returned back into the column head as back flow and part of it is drawn off. A specific feature of the method according to this invention is low ethyl alcohol content in the distillate, which content is lower than what would correspond to the concentration in the ethyl acetate-ethanol-water ternary azeotrope. This fact significantly facilitates final purification of the distillate product to one of commercial purity by a not very demanding subsequent distillation. The water phase containing a quantity of dissolved ethyl acetate and eventually ethyl alcohol is drawn off. The dissolved ester and alcohol can be stripped off from this phase and both components can be returned back into the process. The excessive acetic acid is drawn off from the column boiler continually. The method according to the present invention makes it possible to separate all water produced by chemical reaction in the form of distillate or to withdraw a part of this water from the system as the bottom product together with the unreacted residual acetic acid.